import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class ImgServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //让浏览器5秒自动刷新
        resp.setHeader("refresh", "5");
        //在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();//笔
        //设置图片的背景颜色
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0, 0, 80, 20);
        //给图片写入数据
        graphics.setColor(Color.BLUE);
        graphics.setFont(new Font(null, Font.BOLD, 20));
        graphics.drawString(makeNum(), 0, 20);
//        告诉浏览器这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
//        不让网站有缓存
        resp.setDateHeader("expires", -1);
        resp.setHeader("Cache-Control", "no-cache");
        resp.setHeader("Pragma", "no-cache");
//       把图片写给浏览器
        ImageIO.write(bufferedImage, "jpg", resp.getOutputStream());
    }

    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer stringBuffer = new StringBuffer();
        for (int i = 0; i < 7 - num.length(); i++) {
            stringBuffer.append("0");
        }
        num = stringBuffer.toString() + num;
        return num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
